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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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MALASPINA GLACIER                                         43
was clearly indicated, from Blossom Island southeastward, by the crevassed ice of the Marvine lobe, and it was evident that the Hayden Glacier contributed little to the ice supply of the Malaspina. On emerging from its mountain valley the Hayden Glacier spreads out, and in 1906 its crescentic outer boundary was shown with almost diagrammatic clearness by the change in condition between the smooth surface of the ice contributed by the Hayden and the broken, crevassed ice of the Marvine lobe. Besides pushing out into the Malaspina, the current of the Hayden ice is deflected southeast-wards along the western base of the Floral Hills, giving rise to a narrow, wedge-shaped area which in 1906 was uncrevassed, in striking contrast to the ice of the Malaspina to the west and south of it. The Kwik River emerges from its subglacial tunnel at the point of contact between the Hayden wedge and the Marvine lobe.
We have no definite knowledge of the rate of motion of any part of the Malaspina Glacier but from Russell's description, and from our briefer study of it we are confident that there is great difference in rate of motion in different parts. In the crevassed Guyot lobe there must be rapid movement down to the sea; and that there is rapid motion where the great valley glaciers emerge from their mountain valleys is indicated by the crevassing there, as shown by the Abruzzi photographs of the debouchure of Seward Glacier, by the enormous ice plateau which they supply and maintain, and by areas of crevassing in the valley portions of the tributary glaciers. From these extremes there is every gradation in rate of motion to complete stagnation in interlobate areas and in those portions of lobes where the ice has spread out farthest; but throughout the greater part of the ice plateau there must be some motion in order to keep up the supply. That this motion is not rapid, however, is indicated by the general absence of extensive crevassing. In general the surface of the Malaspina Glacier during the period of observation, up to 1906, was smooth and slightly broken. There were of course some cracks, and some areas of crevassing, there were moulins, and there was roughness due to differential ablation; but that there was a condition of general smoothness, as glaciers go, is indicated by the successsful use of the Malaspina Glacier as a highway of travel and transportation of supplies, partly by sledges, by all the expeditions, over several routes.
In winter the entire surface of the glacier is buried beneath a thick blanket of snow, and from much of its surface this is melted off by the first of August, but patches remain in protected places throughout the summer. The snow line on the Hayden Glacier, according to Russell, lies at an elevation of 2500 feet, which brings it well up in the mountain valley tributaries of the glacier. This agrees with our observations of 1905 when the snow line was above Floral Pass late in August, and in 1906, when we found the snow line just below Floral Pass, in July. In 1905 its elevation was above 1500 feet at least, but in 1906, owing to an accident to our barometers, we were unable to determine its elevation. While some of the higher parts of the Malaspina Glacier may rise above snow line, especially near the mountains, most of its ice surface is exposed to melting during a part of the summer. In the lower, outer portions, the summer ablation continues through several months, but on the higher portions, near the mountains, the period of ablation is very brief. Observations on Hayden Glacier between Floral Hills and Blossom Island, in late July, 1906, showed a rate of ablation of about 4 inches a day and at this point the water on the ice froze as soon as the sun sank low in the western heavens. The rate and extent of ablation on this glacier is so great that unless it were in motion throughout